Processes of separating nitrile-hy-drocarbon mixtures by means of carboxylic acids



Patented Jan. 31," i939 PATENT OFFlCE f rnocnssa s or snrmrmo unrruans mans-mt ar means or aim-mg.

Serial nasal.

11L, al'llgnors to Armour and company,

.11 a corporation of lllinoi's Original muss my a- 1m. Divided and an. nv

cation I October 1, 1,37, M8] N0. 189,212

comm. (c1. see-m) productive source of the lower nitriles is the This invention relates to processes of separating aliphatic nitriles from admixtures thereof with hydrocarbons and it comprises processes wherein'sfu'ch mixtures are treated with a preferential solvent material for the nitriles to tormr an extract phase containing the nitrile dissolved in the solvent and a hydrocarbon phase,-the two phases separated and the nitrile then separated from the extract phase. I

1 --Recently processes have been described, as in U. S.'Patents'1,991,955,'2,038,538 and 2,033,587, for preparing nitrilesof relatively low molecular weight from nitriles of high molecular weight. For example, by methods of pyrolysis higher aliphatic nitrilessuch as steam and palmitonitrile can be cracked to give reaction products cone taining nitriles having four, flve, six and seven" carbon atoms. The cracking operation canbe so controlled that nitriles ofalmost any:desired number -'of carbon atoms say from six to eleven can be prepared from nitriles of; higher .molecularweight. In these processes the reaction products are homogeneous liquid mixtures containing various nitriles associated with quantities of aliphatic hydrocarbons.

Although the cracked reaction mixtures have many uses as such without further treatment,

' there are many instances-when it is desirable to separate the nitriles from the hydrocarbons and to then fractionally distil the separated nitriles. This will yield substantially pure nitriles. And the pure nitriles are starting materials for many organic syntheses since theyare sources of .polar aliphatic compounds having from six to about eleven carbo'natoms. Hitherto j reactive'compounds of this nature have not been available on a commercial scale and at a price which would enable them to be used in great quantities. In' other words, the development of processes of preparing nitriles from the cheap fatty acid' sources has made it possible for us to supply large quantities of aliphatic compounds having from aboutkflve toten carbon atoms in a the alkyl group, together with a highly reactive stant boiling mixtures-aracists-incgl in many'instances-and thereareother objections. l fiemost sired 'lower nitriles. But, as stated, the cracked products contain quantities of hydrocarbons.

mixtures of nitriles and hydrocarbons can be Consequently. we have set ourselves to theproblem of discovering methods by which" these separated to obtain the nitriles which can then bepiractionally distilled if desired. And we have discovered that mixtures of this type can be treated with preferential solvents in such a man-- her that the nitrilesare dissolved to the exclusion of the hydrocarbons. From the extract phase of nitriles and solvent we can then recover the nitriles and recover the solvent for re-use.-

Many experiments have been necessary, however,

since what will or will notact as a preferential solvent for such mixtures could not be determined J in advance of experiment. Many solvents which might seemingly dissolve thenitriles without affecting the hydrocarbons actually .form homogeneous mixtureswithout leading to the formation of stratified layers of hydrocarbon and nitrile extract. Because of the pronounced mutual solubility of the nitriles and aliphatic hydrocarbons,- many solvents dissolve the nitrile but the nitrile acts as a mutual second solvent for both hydrocarbon and added solvent. This leads to mutual solution of all constituents. Consequently, the search for satisfactory preferential solventshas been a diflicult task and many unexpected discoveries have been made.

For example, we have discovered thatwatery solutions of aliphatic alcohols can be used successiully provided care. is taken to control the quantity of water present. Thus, a 75 percent solution of'methyl alcohol will dissolve the nitrile, but not the aliphatic hydrocarbons present but .85 percent methyl alcohol forms a homogeneous solution of alcohol, water, nitriles, and hydrocarbons. Hence',jthe application of the broad, old, idea oi preferential extraction with a suitable solvent to mixtures of the type with which we are polar, or CH. group. This means. thatinany.

concerned has not been a simple matter.

Moreover, having discovered a suitablepreferentw'al solvent which will give an extract containing nitriles dissolved in the solvent, the next step is the liberation of the dissolved nitrile from the'extract. Here again many solvents, apparently suitable as preferential solvents must be discarded becauseof the diill'culties in separating the nitrile therefrom. 'What we have sought-is solvents which would dissolve the nitriles but not the hydrocarbons, whichwould give good tract layer, would then liberate the nitrile.

These requirements havemade the search for solvents prolonged.

We have, however, discovered four classes of compounds'which can be used in our process and, since we are the first to deal with this problem, and to describe its solution, we claim our invention broadly in the appended claims. We believe ourselves to be the first to propose the use of preferential solvents in this art in such a manner that the nitriles are liberated. from the extract phase by the addition of substances thereto which decrease the solubility of the preferential solvent for the nitrile in the extract.

;We have discovered that aliphatic alcohols, phenoliccompounds like phenol and the cresols, amino compounds generally aliphatic but including aniline, and the water soluble aliphatic carboxylic acids can be used under certain condiv tions as preferential solvents and that from the extract phase composed of solvent and nitriles we can separate the nitriles simply by adding something to the extract which acts to decrease the solubility. of the .nitriles'.

We shall first describe our invention with reference to the use oi the aliphatic alcohols. All of the alcohols whichwe use are miscible with water and among them we can use methyl, ethyl, propyl, bothnormal and iso, butyl, benzyl, furifuryl, tertiary butyl, secondary butyl, allyl, di-

amyl secondary amyl and cyclohexyl. When using the;alcohols wefirst treat the mixture of nitriles and hydrocarbons with a watery solution of the alcohol, the amount of water present being suchthat the nitriles are soluble in the watery alcohol but the hydrocarbons are not. We then separate off the upper layer of hydrocarbons from the lower extract phase composed of nitriles dissolved in the watery alcohol. Upon the addition of more water to the extract so as to decrease the actual concentration of alcohol the nitriles separate out since they are not soluble in extremely :diluted alcohol.

These hydrocarbons still contain some nitriles and are advantageously re-extracted with 100 parts of 80 percent methylal'cohol The hydrocarbon'laye'r is again separated and again extracted with ,100 parts by volume of percent alcohol. The final hydrocarbon layer, amounting to 60 volumes, contains only 0.1 percent nitrogen.

, The three alcoholic lower layers, or extract phase, from the three extractions are united and water'add'ed thereto until ,the nitriles therein separate as an upper layer which can be readily decanted. This upper layer amounts to 40 parts and has a nitrogen content of 8.9 percent. The

methyl alcohol layer, after dilution as described,

has a concentration of about 60 percent methyl It can be recovered for reuse by distillation.

Instead of using three extractions with increasing strengths of alcohol we can extract directly with 80 percent methyl alcohol and get good results. Or the 80 percent methyl alcohol can aieppoa run into the top of a column of the nitrile-hydrocarbon mlxtureand the extract phase recovered continuously from the bottom of the column.

However, the strength of alcohol must be closely regulated so that it is strong enough to dissolve nitriles but not hydrocarbons.

We find it desirable to start with fairly dilute alcohol, such as 75 percent strength and 'then reextract the separated hydrocarbon layer with alcohol of increasing strength. The more dilute manner and the-same concentrations as methyl alcohol. When using the other alcohols described above preliminary experiments should be run 'to determine the appropriate strength of alcohol for the extraction. This can be readily done on a small scale before treating large volumes of nitrile-hydrocarbon mixture.

We shall now describe modifications of our invention using aliphatic carboxylic acids as preferential solvents. All the acids we use are miscible at least to some extent with water. Among them can be mentioned the following. Acetic, pro

picnic, acrylic, iso-valeric, normal valeric, isobutyric, normal butyric and caproic.

This modification is well illustrated by refer-.

ence to the use of acetic: For example, we mix parts of nitrile-hydrocarbon mixture with 100 parts of glacial acetic acid containing 4 parts of water.- The mixture is cooled to 0 C. at which temperature stratification occurs. The upper layer or phase is composed of 56 parts of hydrocarbons containing 1.3 percent nitrogen. The lower layer or extract phase amounting to 144 Dartscontains the acetic acid and nitrile. Tothis lower layer we add 100 parts of waterwhich results in the separation ofan upper layer After the lower I amounting to 52 parts which consists essentially 5 of nitriles and contains 5.5 percent nitrogen.

Any acetic acid present can be removed from the nitrile layer by washing with water. The hydrocarbon layer can again be extracted with the from. All quantities above are parts by vvolume.

As stated above, phenols are also suitable solvents. Among them we can use ordinary phenol, and ortho, metal, and para cresols. For example, we mix 100 parts by volume of the cracked nitrile. mixture with 100 parts by vol- ,us 64 parts by volume of nitriles containing 6 percent nitrogen: If desired the -hydrocarbon layer can again be extractedwith more phenol solution.

Many different amines can also be used as preferential solvents. Among them may be mentioned aniline, ethyl amine; isopropyl amine, normal propyl amine, diethyl amine, allyl amine,

50 strongacetic acid to recover more nitrile there- I .bnzyl amine, secondary bu'tyl amine. isobutyl amine, normal butyl amine. isoallyl amine, nor- 'maiflamyl amine, dinormal propyl-amine. pyridine, diallyl amine and cyclohexyl amine. For

example 100 partsby volume. of the -nitrile hydrocarbon mixture is mixed with 100 parts by .-yo1ume,of aniline and the mixture cooled to .0

C. This gives an upper layer consisting of 40 of hydrocarbons containing 0.5 percent nitrogen and a lower layer composed of. 160 parts By volume containing aniline and nitriles. Tothis-lower layer. we. add dilute hydrochloric acid solution until the nitriles separate out. This gives us 60 parts of a nitrile fraction containing '5 percent of nitrogen. The"aniline can be 'recovered for reuse by treating the solution of aniline. hydrochloride with, dilute caustic soda. -In the appended claims we denote the layer of nitrilesdi'ssolv'd in the preferential'solvent asthe extract phase.

This application. is a'division of four co-pending application Serial No. 89,850 filed July 9,

1936, wherein we specifically claim the use of aliphatic alcohol solutionsas preferential solvents. j v

- Having thus described our invention, what we claim is:

. 1. The process of separatingfaliphatic nitriles from admixtures thereof with hydrocarbons which comprises treating the mixture with a Y preferential solvent composed of a mixture of -bon atoms.

a lower aliphatic carboxylic acid and a small amount of water to form an extract phase containing the nitriles dissolved therein and a hydrocarbon phase, separating the phases, adding enough water to'the extract phase togliberate nitriles therein as a layer, and separating the nitrile layer.

- 2. The process as in claim. 1 wherein the mixture of aliphatic carboxylic acid andwater comprises an aqueous mixture of an aliphatic carboxvlic acid having from two to six carbon atoms.

3. The, process as in claim 1 wherein the allphatic carboxylic acid is acetic.

4.- The process of separating aliphatic nitriles from mixtures thereof with aliphatic hydrocarbons resulting from cracking relatively high molecular weight fatty acid nitriles which comprises extracting said mixture with a mixture of a lower aliphatic carboxylic acid and a small ar'nount of water to form an extract phase containing the nitriles dissolved therein in a hydrocarbon phase,

separating the phases, adding enough water to the extract phase to liberate nitriles therein as a layer, and separating the nitrile layer. 5. The process as in claim 4 wherein the aliphatic carboxylic acid has from twoto six car- 6. The process as phatic carboxylic acid is acetic.

ANDERSON W. RALSTON. WILLIAM O. POOL.

in claim 4 wherein the ali- 

